Production of styrene by dehydrogenation of ethylbenzene is commonly conducted by mixing ethylbenzene with steam and passing the mixture through a dehydrogenation catalyst-packed bed. Since the dehydrogenation reaction of ethylbenzene is an endothermic reaction, temperature decreases with the progress of the reaction. In addition, hydrogen generated by the dehydrogenation reaction increases the concentration of hydrogen in the produced gas. These changes adversely affect the dehydrogenation reaction, and hence, the reaction rate is gradually lowered with the progress of the reaction.
In order to solve the above-described problems, there have conventionally been proposed a method of mixing the reaction-produced gas effused from the dehydrogenation catalyst-packed bed with oxygen, passing the mixed gas through an oxidation catalyst-packed bed to selectively combust hydrogen in the reaction-produced gas, and again passing through the dehydrogenation catalyst-packed bed (see Japanese Patent Laid-Open Nos. 130531/1985 and 225140/1986).
According to this method, the reaction-generated gas effused from the oxidation catalyst-packed bed contains a decreased concentration of hydrogen and is at an elevated temperature due to the heat generated by the combustion of hydrogen, and hence the dehydrogenation reaction can again be conducted at a high reaction rate. Therefore, use of a reaction apparatus wherein the dehydrogenation reaction-packed bed and the oxidation catalyst-packed bed are disposed alternately enables to finally attain an extremely high conversion of ethylbenzene.
However, one of the problems with the process of producing styrene by dehydrogenation of ethylbenzene using the combination of dehydrogenation reaction and oxidation reaction is that yield of styrene is seriously reduced after a long period of operation.